When you make a call with a SIM that has MEX enabled, all calls are sent to the API.
All calls made to your MEX enabled cellphone number are also routed to to the API. As
a result all calls are handled by the voice_start parameter on the number object.
You may use all the functions in the API on all calls.
To forward the call to a phone you need to make a connect action to the phone number.
Calls to the MEX phone number from the API will be connected to the phone with the SIM inside.